The diagram represents a potentiometer circuit that is being used to compare the electromotive forces (e.m.f.), $E_1$ and $E_2$, of two cells. $XY$ is a resistance wire with uniform resistance. The fixed resistor has resistance $R$. A sliding contact is then moved along wire $XY$. When the sliding contact reaches position $P$, the galvanometer shows zero. The circuit is altered so that the galvanometer again shows zero, but now when the sliding contact is at a different position to the left of $P$. Which change could have been made to the circuit?
- AThe wire $XY$ was replaced with one of lower resistance.
- B$E_2$ was increased.
- C$E_1$ was decreased.
- D$R$ was decreased.